全文获取类型
收费全文 | 84270篇 |
免费 | 4698篇 |
国内免费 | 56篇 |
专业分类
林业 | 2928篇 |
农学 | 2279篇 |
基础科学 | 568篇 |
9217篇 | |
综合类 | 15291篇 |
农作物 | 3086篇 |
水产渔业 | 3916篇 |
畜牧兽医 | 45780篇 |
园艺 | 881篇 |
植物保护 | 5078篇 |
出版年
2018年 | 1036篇 |
2017年 | 1174篇 |
2016年 | 1089篇 |
2015年 | 937篇 |
2014年 | 1179篇 |
2013年 | 3072篇 |
2012年 | 2138篇 |
2011年 | 2723篇 |
2010年 | 1665篇 |
2009年 | 1761篇 |
2008年 | 2630篇 |
2007年 | 2436篇 |
2006年 | 2447篇 |
2005年 | 2151篇 |
2004年 | 2115篇 |
2003年 | 2102篇 |
2002年 | 2011篇 |
2001年 | 2721篇 |
2000年 | 2820篇 |
1999年 | 2136篇 |
1998年 | 819篇 |
1997年 | 824篇 |
1996年 | 809篇 |
1995年 | 1032篇 |
1994年 | 906篇 |
1993年 | 857篇 |
1992年 | 1940篇 |
1991年 | 2092篇 |
1990年 | 1925篇 |
1989年 | 1937篇 |
1988年 | 1827篇 |
1987年 | 1931篇 |
1986年 | 1976篇 |
1985年 | 1874篇 |
1984年 | 1485篇 |
1983年 | 1303篇 |
1982年 | 886篇 |
1979年 | 1375篇 |
1978年 | 1126篇 |
1977年 | 974篇 |
1976年 | 939篇 |
1975年 | 987篇 |
1974年 | 1281篇 |
1973年 | 1300篇 |
1972年 | 1241篇 |
1971年 | 1149篇 |
1970年 | 1095篇 |
1969年 | 972篇 |
1968年 | 839篇 |
1967年 | 872篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Pack DH 《Science (New York, N.Y.)》1980,208(4448):1143-1145
93.
94.
95.
96.
Replacement of the drinking water of chicks maintained on a normal mixed protein diet with an aqueous extract containing the equivalent of 5 g of the dried leaves of Solanum malacoxylon (DLSM) per 100 ml for one month produces a hypercalcaemia (23-49 per cent), hypomagnesamia (28-37 per cent), hypophosphataemia (26-34 per cent), hypouricaemia (29-34 per cent) and a decrease in plasma alkaline phosphatase activity (54-98 per cent). The ash content of the defatted, dried tibiae and the body weight of the DLSM treated chicks were also significantly lower (37-7 per cent and 17-79 per cent respectively) than the corresponding values for the untreated birds. The results obtained are similar to those reported for hypervitaminosis D3 in the chick. 相似文献
97.
Sunlight is known to reduce the incidence of blister blight disease of tea, caused by Exobasidium vexans . The effects of the ultraviolet-B (UV-B: 290–320 nm) component of solar radiation on the disease and the development of E. vexans were studied in the field in Sri Lanka using UV-screening filter materials held over a commercial crop. Exclusion of UV-B radiation by Polyester, which reduces fluxes in the UV-B region by approximately 75–85%, increased both the number of translucent spots (immature sites of infection) and number of sporulating blisters (mature sites of infection), but it had little or no effect on the sporulation of the pathogen. When basidiospores were artificially inoculated on leaves, and were exposed to full or filtered solar radiation, their survival and germination increased when UV-B wavelengths were removed; significant differences were found 62 h after inoculation. However, UV-B did not affect the extension of germ tubes. This study indicates that the UV-B component of solar radiation plays an important role in the natural regulation of blister blight disease in the field. 相似文献
98.
Alexander N. Shikov Ekaterina D. Obluchinskaya Elena V. Flisyuk Inna I. Terninko Yulia E. Generalova Olga N. Pozharitskaya 《Marine drugs》2022,20(5)
In recent years, natural deep eutectic solvents (NADES) have been widely investigated for the extraction of food and medicinal plants as well as seaweeds. However, the ability of NADES for trace elements co-extraction from natural sources is not well investigated. The aim of this study was to investigate the ability of common NADES for trace elements co-extraction from Fucus vesiculosus. All of the tested NADES did not recover As and Co (concentration <LOQ). Moreover, all of the tested NADES provided a low recovery (<9%) of Ba, Ca, Fe, Mg, Mn, Sr, and Zn. The method of extraction had not shown a statistically significant effect on the co-extraction of all elements (excluding Ba and Ca). In contrast, the water content in NADES was significantly affected on the recovery of Ba, Ca, Mg, Mn, Sr, and Zn. The recovery of Al and Cr was relatively high and considerably varied (from 1.5 to 59.9%). NADES comprising lactic acid:glucose:H2O (5:3:1) provided the lowest contents of all elements, and the highest extracted amounts were obtained employing water contents of 60–80%. The calculated daily intake of all the elements contained in NADES extracts were less than the daily dose risk estimators. The hazard quotients, hazard indexes, and carcinogenic risk calculated for all trace elements and their combination were considerably less than 1. This evidences no health risk, and carcinogenic risk after topical application of all studied NADES. For the first time, the results of the current study demonstrated that NADES extracts of F. vesiculosus contain a lower amount of trace metals and are safer than the extracts obtained with water and 70% acetone. This indicates a significant advantage for NADES compared with the other solvents. 相似文献
99.
This paper describes the main features of the Sangay wilderness area in the Ecuadorian Andes. It is a region of great diversity with life zones ranging from tundra to subtropical rain forest. The conservation value of the area is assessed and the feasibility of protection determined. Boundaries based mainly on the limits of human interference are put forward with management proposals for its establishment as a National Park. 相似文献
100.